1. The Field of the Invention
The present invention relates to caching content for mobile clients. More specifically, the present invention relates to methods, systems, and computer program products for caching content that has been customized for one or more operating characteristics of a mobile client.
2. Background and Related Art
In past years, access to electronic content, such as email, Web pages, financial data, sports information, etc., typically has occurred from either a home or office computer. These home and office computers may be classified in two broad categories, laptop computers and desktop computers. The selection between laptop and desktop generally depends on the needs of a particular user. Where some level of portability is desirable, laptop computers are the obvious choice. Otherwise, desktops are the usual selection because laptops ordinarily command a price premium based on their relatively small size when compared to desktops having comparable processing capabilities.
More recently, society in general has been placing an ever-increasing value on mobile access to information. Heightened demand for content, both in business and personal settings, has generated a need for content to be available immediately, from almost anywhere at almost any hour. Therefore, access limited to laptop or desktop computing systems presents a substantial detriment. One of the most significant drawbacks with desktop computers is readily apparent: it is impractical if not impossible to carry a desktop computer around as a user moves from one place to another. Thus, access to content via desktop computer is limited to the location of the desktop computer.
While laptops ease the burden imposed by transporting a computer from one physical location to another, they are only a relatively minor improvement in terms of providing constant access to information. Among other things, (i) the size and bulk of laptop computers preclude a user from carrying a laptop on his or her person; (ii) limited battery life prohibits constant operation; (iii) boot time makes quick content access impractical; and (iv) laptops usually are connected to a specific network, covering a relatively small geographic area. In short, laptops provide a sensible solution for intermittent access to content, but are ill-suited for constant mobile access.
In contrast, truly mobile devices, such as telephones, pagers, personal digital assistants (“PDAs”), and the like, are easily placed in a purse or pocket, operate for many hours by switching to a standby mode when not in use, require no boot time, and use wireless protocols, covering large geographic areas, for communication. Initially, limited processing and display capabilities constrained telephones and pagers to voice or small amounts of text. While PDAs provided more processing and display characteristics, only short-range, infrared, wireless connections were available. However, as the demand for constant mobile access to information has become more pronounced, the once-separate technologies of computers, telephones, pagers, PDAs, etc., are converging. For example, the displays, processing, and memory of telephones and pagers are increasing, and PDAs are supporting telephone- and pager-like communication links.
Nevertheless, the rapidly changing technology of mobile devices presents a number of significant obstacles to providing constant mobile access to information. In particular, the operating characteristics of mobile devices vary greatly. For example, various operating systems, application software, and the like, may represent data differently, support different data fields, and/or support different file types. Differences in hardware impose further barriers in furnishing constant mobile access to information. In spite of the technology convergence mentioned above, telephones typically have the least amount of display area, followed by pagers. PDAs generally have more display, memory, and processor power than either telephones or pagers, but these characteristics vary substantially from one PDA to another.
Even for mobile devices having similar display, memory, and processor capabilities, the assortment of communication links and software that are supported by mobile devices often requires one device to be treated differently from another. As a result, content may need to be tailored or customized for each specific device receiving or requesting content. For example, an email delivered to a telephone may only include textual content based on the display capabilities of the telephone, whereas the same message delivered to a laptop computer may include the textual content and some attached multimedia content. Email software on one telephone may support only certain data fields or file formats for attachments, and may require an underlying data format that is different as compared to other telephones. Similar issues exist for other types of content, such as Web pages, financial data, sports information, meeting reminders, calendars, contacts, mailbox summaries, configuration data, etc., due to the wide variety of operating characteristics found in mobile devices.
While customizing content based on the device that will receive the content is desirable, customization leads to problems of its own. For example, email servers often operate at near capacity. Introducing the additional processing necessary to customize content by device operating characteristics may degrade server performance beyond tolerable limits. Furthermore, implementing the customization at an email server requires changes to the email server for each new type of mobile device that becomes available. Frequent changes to email server code imposes substantial coding and testing responsibilities on developers, due to the already complex nature of email servers. Moreover, already overburdened information systems staff are forced into essentially constant upgrade cycles as developers release new software, especially for rapidly advancing technologies like mobile devices. Other types of content servers suffer from similar considerations.
Caching of customized content may reduce some of the additional processing burdens, but prior art caching techniques may prove inadequate. For example, caching typically involves creating a copy of content that is ordinarily stored elsewhere. The cached copy satisfies requests for the content in less time than would be required to access the usually slower system that is responsible for storing the content. Nevertheless, because the cached copy and the stored copy are identical, caching is transparent to the content requestor. The requestor is aware only of receiving the content that was requested.
Consider then, a mobile device requesting content. Using traditional caching techniques, the mobile device must ask for the customized version of the content because a request for the content itself would require transforming the content before sending it to the mobile device, and repeating the customization for each request is likely to impose significant processing overhead. To realize any significant benefit from caching, the mobile device should request the customized version of the content rather than the content itself.
However, it is undesirable for mobile devices to request customized content for at least two reasons. First, the customized content may not exist. For example, if the content is new and has not been requested previously, the content may not have been added to the cache. Alternatively, the customized content may have been removed from a cache based on comparatively infrequent requests. Whatever the reason, at some point in time it is very likely that the customized content will not be available in the cache, leading to what is known to those of skill in the art as a cache miss. In traditional caching, cache misses are a normal and expected part of cache operation. When a cache miss occurs, the request is redirected to the system responsible for storing the content. In the case of customized content, this requires storing a permanent version of the customized content so that cache misses may be redirected to the permanent version. Obviously, by requiring a permanent version, all content that will be accessible to a mobile device should be customized prior offering access to the mobile device. In other words, a complete copy of the content, customized for the mobile device, should be created to implement traditional caching.
A further problem with mobile devices specifically requesting customized content is that it precludes the customization from being transparent to the mobile devices. Rather than requesting content and allowing the source to determine how the content should be altered for a particular device, the device requests the content that the device believes is best suited for its operating characteristics. As new or enhanced ways of customizing content become available, the mobile device must be configured so that subsequent requests are directed to the new or enhanced content.